Non-impact, or ink jet, recording is becoming popular as a method for converting image data in the form of electrical signals into hard copies because it produces less noise during recording than does impact recording.
The ink jet method is also useful because it uses ordinary paper without the need for a special process, such as fixing, for recording purposes.
The ink jet method which has already been put to practical use involves filling an airtight container with ink, applying a pressure pulse to the container, and sending the ink out of the orifice of the container in a jet for recording purposes. The ink jet apparatus in such a method cannot be made compact in view of its operating mechanism. Such apparatus requires mechanical scanning to record at a desired image density, which causes the recording speed to be reduced.
At the same time, there have been proposed techniques for remedying shortcomings in past ink jet printing methods and making high-speed recording possible.
The magnetic ink jet method is a typical example of such improvement, which comprises arranging magnetic ink close to a magnetic electrode array, forming an ink-jet state corresponding in position to a picture element by making use of a swell of the ink in the presence of a magnetic field, and jetting the magnetic ink in the static electric field. Since this method admits of electronic scanning, high-speed recording becomes possible, but it is still disadvantageous in that not only the selection of ink but also coloration characteristic of the ink jet method is difficult.
In addition to the aforesaid method, the so-called plane ink jet method is also well-known. This method involves arranging ink in a slitlike inkholder in parallel to an electrode array, and letting fly the ink in accordance with an electric field pattern formed between an electrode facing the electrode array through recording paper. Since no minute orifice for storing ink is required in this method, ink clogging can be prevented. However, high voltage applied for jetting the ink makes it necessary to drive the electrode array on a time division basis to prevent a voltage leak across the adjoining or neighboring electrodes; the disadvantage is that the recording speed cannot be increased to the extent intended.
There has also been proposed the so-called heat bubble jet method for jetting ink out of an orifice by means of thermal energy. In this method, the ink is abruptly heated to cause film boiling and a pressure rise resulting from the rapid formation of bubbles within the orifice is utilized to jet the ink out thereof. However, the film boiling temperatures are as high as 500.degree.-600.degree. C. and this makes it difficult to put the aforesaid method to practical use because the ink properties tend to be changed by heat, and because the heating resistor protective layer provided as a heating means is deteriorated.
As set forth above, there are remaining problems to be practically solved in any of the ink jet methods heretofore developed, the problems including difficulty in sufficiently increasing recording speed, necessity of employing special ink and contriving a particular driving means, and thermal deterioration of the ink and the heating means.